fix: don't invoke if no args

src/command.c

@@ -5,7 +5,7 @@
 
 unsigned char invoke(struct Args args) {
   pid_t child = fork();
-  if (child == 0 && args.argc > 0) {
+  if (child == 0) {
     execvp(args.argv[0], args.argv);
     return 1;
   }

src/main.c

@@ -18,7 +18,10 @@ int main() {
     struct Args args = parse(input_line);
     free(input_line);
 
+    if (args.argc > 0) {
       invoke(args);
+    }
+
     {
       unsigned int i = 0;
       while (i < args.argc) {